This application is based on patent application No. 11-64489 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a projection image display device disposed in front of the eyes of an observer, and specifically relates to an image display device providing a wide viewing angle image.
2. Description of the Related Art
Projection image display devices used in front of the eyes of an observer are either head-mounted displays or hand-held displays. This type of projection image display device is provided with a enlarging optical system to provide a wide field of view image having a high sense of realism, and enlarges a projection image displayed on a display unit and projects this image as a virtual image on the eye of an observer.

For example, U.S. Pat. No. 5,844,713 discloses a projection image display device providing a plurality of display units in an array and which enlarges the projection image displayed on all display units via a single enlarging lens. Projection image display devices are known wherein display units and enlarging lens units are arranged in a plurality of arrays to individually enlarge the projection image displayed on each display unit and projects these images on the eye of an observer. In any of these devices, image signals representing part of the projection image are transmitted to each display unit so as to compose a single image in its entirety.
These devices can provide a wide field of view and sharp and nearly identical images at any part of the image. Since these devices are provided with a single large lens or a plurality of lenses as an enlarging optical system, it is difficult to obtain a compact and light weight device desired for use as a head-mounted display device or a hand-held display device.
Furthermore, well-defined recognition of two points by an observer is restricted to within a narrow range encompassing the main viewpoint, such that even when displaying an image with a wide viewing angle an observer cannot clearly perceive the entire image. Although it is unnecessary to sharply see the entire image in order to increase the sense of realism, conventional devices increase the size and weight of the device in order to clarify these unnecessary ranges.
In view of these previously mentioned disadvantages, an object of the present invention is to provide a projection image display device both compact and light weight and providing an image in a wide field of view.
These objects are attained by a projection image display device comprising a first display unit for displaying a first image based on a first image signal; an enlarging optical system for enlarging the first image and projecting the first image to the eye of an observer; and a second display unit disposed for displaying a second image based on a second image signal and directly projecting second image to the eye of an observer.
This projection image display device is provided with a first display unit and a second display unit, and is capable of providing a projection image representing a wide range by using the first image signal and the second image signal supplied by the first and second display units as signals representing adjacent parts within the same image. In this image, the part displayed by the first display unit is projected to the eye of an observer as a virtual image through the enlarging optical system, and the part displayed on the second display unit is projected as a real image directly to the eye of the observer.
The projection image of the first display unit viewed by the observer is positioned a suitable distance in front of the eye, and the projection image of the second display unit is projected nearby the first image such that the observed field of view is a wide field of view. At this time, the projection image of the second display unit is not sharply projected since there is a difference between the distance to the virtual image displayed by the first display unit and the distance to the real image displayed by the second display unit. However, this lack of sharpness in the projection image of the second display unit is not perceived as an unnatural image by the observer who is focused on the projection image of the first display unit. Accordingly, the observer perceives a high sense of realism similar to when the projection image of the first display unit and the projection image of the second display unit are positioned at equal distances.
Since the enlarging optical system directs only the light of the projection image of the first display unit to the eye of the observer, a small diameter lens, or a single lens may be used. Accordingly, the projection image display device can be compact and light weight. The second display unit may comprise two or more units, such that the field of view may be increased by using more display units.
Image signal control means may be provided in the projection image display device to control one or both of the first image signal and second image signal so as to project the projection image of the first display unit and the projection image of the second display unit at identical size to the eye of an observer. Furthermore, image signal control means may be provided to control one or both of the first image signal and second image signal so as to project the projection image of the first display unit and the projection image of the second display unit at identical brightness to the eye of an observer.
If the first image signal and the second image signal are not subjected to any image processing, differences are generated in the size and brightness of the images of the first and second display units projected to the observer in accordance with the size of the display surface of both display units, and the magnification ratio of the enlarging optical system. The image signal control means can prevent this difference from being generated by linking the size and brightness of part of an image displayed on the first display unit and part of an image displayed on the second display unit so as to obtain a natural projection image.